Improve Quarkiverse platform update process on release

[metacosm]

Currently, the process is not covering all cases, which leads to missed platform updates opportunities and frustration because platform PRs then need to be opened manually.

We should extend the project.yml metadata so that it also includes which platform branches are targeted by a given release as this would make things more explicit and allow branches to be "locked" to a given Quarkus major (e.g. LTS version).